There is a very large quantity of plastic pipe and duct used in numerous industries because of their beneficial corrosion resistance to a broad range of aggressive chemicals. Almost all plastic pipe and duct are limited in how long a length of material can be shipped, usually about twenty to a maximum of sixty feet long. These pieces are invariably fastened together at a jobsite to make longer lengths and/or connections to fittings. There are also a number of different means of joining them, including built in slip fittings or couplings, particularly with small diameter materials. Usually some sort of adhesive may be used which xe2x80x9cmeltsxe2x80x9d the base material of the pipe or duct, such as PVC, thereby making a chemical connection. Alternative means is by screw threads on the pieces of duct or pipe similar to those used for steel pipe, or flanged connections. Applicant""s U.S. Pat. No. 5,909,904 for Flange Joint Assemblies discloses new and improved mechanical flange connections for plastic pipe or duct.
Many of these cannot be used easily or cost effectively on fiberglass pipe or duct, particularly on large sizes such as 60 inch or 1.5 meters in diameter. Flanged joints are often used but these are very expensive. Normally the two pieces of connecting pipe or duct are sanded on their exteriors, and over wrapped with fiberglass or other materials which is saturated with a desired resin. This resin hardens to make a hopefully leakproof joint. The ability of achieving the latter depends on the skill of the applicator and the quality of the materials.
There are normally two different types of fiberglass joints, the butt and wrap joint (A) and the bell and spigot joint (B) as depicted in FIG. 1. In the butt joint the ends of each piece of pipe or duct are cut and have their ends squared off and are of the same size. Various means such as metal clips are used to hold the assembly together until such time after the glass and resin are applied and the resin hardens. The metal clips are left inside the assembly, which rot out prematurely causing early joint leaks in the system.
Alternatively, a bell and spigot joint (B), as depicted in FIG. 1, may be used; here one end of one piece of duct or pipe is full diameter. The mating end of the connecting duct has been enlarged so that its inside diameter is sufficient to accept the outside diameter of the connecting piece. Again some method of holding the assembly together is used until the exterior of the joint may be sanded, the resins mixed, and for glass or other materials to be wrapped around the joint, saturated with resin, and the resin hardens.
The process of making these joints is messy; glass particles get inside workmen""s clothes, and irritate their skin, and often the resin not only has an unpleasant odor, but may be toxic, carcinogenic or cause rashes. The present invention is a unique and improved joint assembly and method of making these joint assemblies which is simpler, quicker and less expensive than making xe2x80x9cnormalxe2x80x9d butt and wrap joints, bell and spigot joints or flanged joints in the field.
Briefly stated, the present invention provides a joint assembly for connecting together cylindrical plastic pipe or duct sections, preferably fiberglass pipe or duct sections. The pipe or duct sections generally are about twenty to forty feet in length and have a diameter of up to about one hundred and twenty inches. An internal tubular slip collar having a diameter slightly less than that of the pipe or duct sections fits into their opposing abutting end interiors joining the sections end to end. An external tubular slip collar having a diameter slightly greater than the pipe or duct sections is mounted over the joined opposing abutting pipe or duct sections encircling their exterior surfaces. A special non-volatile organic epoxy resin adhesive, non-VOC, has been previously applied in the joining of the mating surfaces of the internal and external slip collars and the pipe or duct sections providing a double adhesive sealed and three level permanent joint previously unobtainable.